1. Field of the Invention
The present invention generally relates to surgical cable systems and the like. More particularly, an embodiment of the invention relates to a method and apparatus for securing surgical cable around a portion of a human bone.
2. Description of the Related Art
Surgical cables are used in a variety of surgical procedures, some examples include: spine surgery; total hip arthroplasty; fracture fixation; closure of the sternum following open heart surgery; and oral/facial surgery to repair mandibular fractures. In these and other surgical procedures the cable may be used to set and secure bone portions in the proper orientation during the healing process.
Fractures of the vertebrae in the spinal column are very difficult to immobilize, often requiring the use of internal pins, cables and/or rods. One frequently used procedure involves wiring the fractured vertebra to one or more adjacent vertebrae to secure the vertebra in an ideal position for healing. Another method involves wiring the fractured vertebra to a rod that is similarly joined to other vertebrae. Both of these methods, as well as other techniques for spinal repair, rely on the use of cables which are secured around a portion of a vertebra.
A number of methods for encircling bone portions with surgical cables have been developed. Most of these techniques involve passing a cable around a portion of the bone and securing the cable in position using a crimp. Examples of cabling apparatus and methods are illustrated in U.S. Pat. Nos. 4,966,600; 5,395,374; 5,415,658; 5,423,820, and 5,569,253. Each of these patents is incorporated by reference as if fully set forth herein.
The Acromed(trademark) Cable System by Songer, as shown in U.S. Pat. No. 4,966,600, represents a cabling system that relies on the use of a metal crimp member to secure a cable in a loop. In one embodiment of the Acromed(trademark) system a crimp member is affixed to one end of the cable. The cable may then be passed partially through a connector. The crimp member may inhibit the cable from passing entirely through the connector. The cable may then be looped around the bone portion and passed again through the connector. A tensioning device is used to tighten the cable around the bone portion, and another crimp member is applied to the portion of the wire extending out from the connector to fix the cable in position.
The Acromed(trademark) system relies on crimp members to attempt to irreversibly secure the cable in position. This feature may present difficulties if a number of cables are used in series since it is often necessary to retighten some of the cables as other cables are added. To overcome this problem a double crimp technique is commonly used. In this technique the cable is passed through two crimp members before the cable is tensioned. After tensioning, the top crimp member may be affixed to the cable. When the cable becomes loosened, it may be re-tensioned and the lower crimp member affixed to the cable. The upper crimp member may be trimmed off after the second crimp member is fastened to the cable. A disadvantage of this approach is that the number of re-tensions that may be performed is determined by the number of crimp members attached to the cable before the initial tensioning. If additional re-tensioning is required after the last crimp member has been attached to the cable, the cable may need to be removed and a new cable attached.
An orthopedic cable apparatus manufactured by Danek Medical Inc., as shown in U.S. Pat. Nos. 5,395,374 and 5,423,820, appears to overcome these problems. The apparatus consists of three separate parts: a double-apertured L-shaped crimp; a cable clamp; and a tensioning tool. The Danek system affixes one end of the cable to the double-apertured L-shaped crimp. The cable is then looped around the bone portion and passed through the other aperture of the L-shaped crimp. The cable is then passed through a cable clamp, and further through a tensioner. The tensioning device is used to tighten the cable around the vertebra. Once the appropriate tension is achieved the cable clamp is tightened to temporarily fix the cable in position. Since the cable clamp acts as a non-permanent securing device, the user is free to re-tension the cable a number of times during use. When the user is finished, the cable is fixed into position by crimping the second crimp portion of the L-shaped crimp onto the cable. The Danek cabling system avoids the need for multiple crimps, as used by the Acromed(trademark) system, however, it still relies on crimps to secure the cable in position.
A disadvantage to the use of crimps for securing a cable in position is that the crimps may be highly unreliable. The crimps are typically compressed by the user to affix them to the cable. However, it may be very difficult to control the percentage of deformation of the crimp such that a predictable and consistent amount of deformation may be produced. If the crimp is over deformed some of the cable strands may be sheared off, reducing the strength of the cable at the connection. Conversely, if the crimp is under deformed, the crimp may be incapable of preventing the cable from loosening after the procedure is finished.
Another problem encountered when using cable systems is that they force the cable into a specific position relative to the point where the cable crosses itself. In some cases there is an advantage for the ends of the cable to be in a parallel orientation. Such an orientation allows a minimal profile of the connector. A low profile width is generally desired to minimize sinus formation and soft tissue irritation. The parallel orientation may sometimes cause a sharp bend in the cable, thereby creating stress in the system. To overcome this stress it is desirable for the ends of the cable to be in a perpendicular orientation relative to each other.
The Acromed(trademark) apparatus, as shown in U.S. Pat. No. 4,966,600, may be used in a number of ways in order to achieve the desired cable orientation. In one method the cable comprises a permanently looped eyelet end. The other end of the cable may be passed through the eyelet to form a loop in which the ends of the cable are oriented in a perpendicular fashion. In another method the ends of the cable may be held in a parallel orientation by using a special connector designed for this purpose. The Danek system, as shown in U.S. Pat. No. 5,569,253, is also designed for use with the ends of the cable in a parallel or perpendicular orientation. The Danek system relies on the use of specially designed connectors for each orientation. Neither the Acromed or the Danek systems describe a single connector which would allow the cable to be positioned in both a parallel and a perpendicular orientation.
The above mentioned methods and systems inadequately address, among other things, the need for an apparatus that allows re-tensioning of the cable, as well as multiple orientations of the cable. The devices also rely on crimps affixed to the cables to hold the cable in place. As mentioned before, such crimps may be unreliable. It is therefore desirable that a cable system be derived that incorporates, in a single device, the ability to allow the cable to be re-tensioned, a non-crimping securing mechanism, and multiple cable orientations.
An embodiment of the invention relates to a surgical cable system that may include a connector adapted to hold a cable in a loop around a human bone element and a tensioner. The connector may include a connector body, a cable, and a pin adapted to secure the cable within the connector body. The term xe2x80x9ccablexe2x80x9d within the context of this application is taken to mean an elongated flexible member. The term xe2x80x9cpinxe2x80x9d within the context of this application is taken to mean an elongated inflexible member.
The connector body may include a first arm and a second arm, an internal cavity, and at least two ducts. In one embodiment, the first and second arms extend from the same face of the connector body such that the connector body is substantially U-shaped. The internal cavity may run longitudinally through the entire connector body and passes in between the two arms. The ducts may be perpendicular to the internal cavity. The ducts either run transversally through the entire connector body (in the case where the connector is coupled to the elongated member), or are formed within the elongated member. The ducts may be oriented such that the ends of a cable, when the cable is passed through the ducts to form a loop, may be oriented in a substantially parallel orientation with respect to each other. The ducts may be located proximate to the internal cavity. In the case where the connector is coupled to the elongated member: the connector body may contain at least one aperture that is positioned between a duct and the internal cavity; the connector body may contain two apertures that connect two separate ducts to the internal cavity; the ducts, the apertures, and the internal cavity are oriented with respect to one another such that a cable passing through the duct may extend through the aperture into the internal cavity.
The cable may be substantially flexible such that the cable may form a loop for engaging a portion of a human bone. The cable may be of a diameter such that the cable may pass freely through a duct. The cable may also be of a diameter such that it may extend from the duct, through the aperture, and into the internal cavity. The cable may include a tip which may inhibit the end of the cable from passing through the duct.
The pin comprises an upper portion and a lower portion. The upper portion may have a diameter that is substantially larger than the diameter of the internal cavity such that the upper portion of the pin is inhibited from passing through the internal cavity. The lower portion of the pin may have a diameter that is substantially less than the diameter of the internal cavity such that the lower portion of the pin fits within the internal cavity.
The pin may be positionable within the internal cavity where it may exert a compressive force against the cable to secure the cable within the internal cavity. The cable may be looped around a bone and through the ducts. Subsequently, positioning the pin within the connector body may secure the cable in place. While the cable is secured the cable is no longer able to move within the connector. The bottom edge of the pin may be deformed to secure the pin within the internal cavity.
In one embodiment, the pin is placed within the internal cavity of the connector body before the cable is threaded. The pin may be secured within the internal cavity by deforming the bottom edge of the pin. Removal of the pin may be inhibited by the deformed bottom edge. The pin may be substantially rotatable while positioned within the internal cavity. The upper portion of the pin may contain at least two flat edges, the edges being oriented on opposing sides of the upper portion of the pin. The distance between the two edges may be less than the distance between the two arms extending from the connector body. The arms may interact with the edges such that rotation of the pin is hindered. The pin may be rotatable when sufficient force is applied to overcome the hindering force of the arms.
The pin may include two grooves. The grooves may be aligned with the apertures, when the pin is inserted within the internal cavity, such that the cable may pass freely through the connector body. The pin may also be rotated, while the pin is inserted within the internal cavity, such that the grooves are perpendicular to the apertures. The rotation of the pin, after a cable has been threaded through the connector body, may exert a compressive force against the cable to secure it within the connector body. The pin may be subsequently rotated to allow free movement of the cable through the connector body.
The pin may further include an opening extending longitudinally through the entire pin. The opening may include a top section and a bottom section. The top section may have a diameter that is substantially greater than the diameter of the end of the cable. The lower section may have a diameter that is substantially less than the diameter of the tip of the cable. The cable may be passed through the opening, with the tip of the cable positioned within the opening, and further through a duct to form a loop. The pin may be positioned within the internal cavity to secure the cable in place, while the cable is passed through the opening and the duct. When secured in this position the cable may be oriented in a substantially perpendicular orientation.
The cable may be passed through the ducts of the connector body such that the ends of the cable are oriented in a substantially parallel orientation. Alternatively the cable may be passed through the opening of the pin and through a duct to form a loop, the ends of the cable being in a substantially perpendicular orientation.
The surgical cable system may also include a tensioner adapted to vary the tension of the cable and secure the cable. The tensioner may include a body, a shaft for contacting the connector, a driver for positioning the pin within the connector body, and an arm for adjusting the shaft.
The shaft may be mounted within the body, such that it extends from both sides of the body. The arm and the shaft may be connected such that the arm is capable of being adjusted to retract or extend the shaft from an end of the body. The body may include a stopper which secures the position of the shaft with respect to the body.
The shaft may include a tip adapted to hold the connector. The tip may include a recessed opening which is shaped to couple to the connector. The shaft may also include an opening extending longitudinally through the shaft. The opening of the shaft may be adapted to allow the driver to pass through the shaft and onto the connector.
The body may include a cable clamp adapted to secure the cable against a portion of the body. The body may include at least two cable clamps. The cable clamps may secure the cable against a portion of the body after the cable is threaded through the connector and around a portion of a human bone. The shaft may engage the connector, after the cable has been secured with respect to the body, such that movement of the shaft causes the tension of the cable to vary.
The driver may include an end adapted to engage the pin of the connector. The driver may include a handle to allow the driver to be moved in a circular motion. The shaft may include an opening, extending longitudinally through the shaft, that allows the driver to engage the pin while the connector is in contact with the shaft. The driver may engage the pin such that rotation of the driver causes the pin to rotate into a position which secures the cable within the connector. While the cable is secured the cable is no longer able to move within the connector. Subsequent to securing the cable, the driver may be rotated to cause the pin to move into a position which allows the cable to once again have mobility within the connector.
In another embodiment, a protrusion may be built onto the upper portion of a pin. The protrusion may be configured to interact with a locking portion built onto the connector body such that the protrusion and the locking portion together inhibit rotation of the pin. The connector body may include a locking portion made up of at least one projection. The locking portion may extend along the side of the connector body. The projection may include an opening for receiving the protrusion.
The protrusion may be oriented away from the locking portion when the pin is in an unlocked position. When the pin is in an unlocked position the cable may be free to move through the connector. When the pin is in a locked position the cable may be inhibited from moving through the connector. In the locked position the pin is positioned such that the protrusion now lies within the opening formed by the projections. The flat edge of the protrusion may engage the flat edge of the projection to inhibit rotation of the pin.
While rotation of the pin in a first direction is substantially inhibited, the pin may be turned in an opposite direction. When rotated in a first direction, the rounded edge of the protrusion contacts the projection of the locking portion to slightly inhibit the rotation of the pin. By applying sufficient rotational force to the pin may cause the projection to deflect slightly outward, providing sufficient space for the protrusion to be rotated past the projection and away from the locking portion. In this manner the pin may be moved into an unlocked position.
In another embodiment, a connector including two locking portions may be used in conjunction with a pin including two protrusions. The first locking portion of the connector may be oriented opposite a second locking portion. The pin may include two protrusions oriented opposite to each other. Each protrusion may include a rounded side and a flat side.
When the cable is to be secured within the connector, the pin may be rotated in a first direction. Rotation in this direction may move the pin into a locking position. When the pin is positioned in this locking orientation the protrusions move into the openings of locking portions. Thus, the action of securing the cable by rotating the pin may move the protrusions into a position such that rotation in a direction opposite to the direction for securing the cable is inhibited.
An advantage of the present invention is that the cable may be secured or movable within the connector as necessary.
Another advantage of the present invention is that the cable may be secured into position without the use of crimps.
Yet another advantage is that the present invention may allow the ends of the cable to be in a perpendicular orientation with respect to each other or a parallel orientation with respect to each other.
The use of two projections and two locking portions has the advantage that the pin may be secured in a locked position whenever the cable is secured within the connector body. Additionally, the two projections may provide increased resistance to rotation of the pin in a clockwise direction when the pin is in a locked position.